Hadith 2437
Narrated One of the wives of the Prophet: Hunaydah ibn Khalid narrated from his wife on the authority of one of the wives of the Prophet ﷺ who said: The Messenger of Allah ﷺ used to fast the first nine days of Dhul-Hijjah, Ashura' and three days of every month, that is, the first Monday (of the month) and Thursday.
Hadith 2452
Narrated Umm Salamah, Ummul Muminin: Hunaydah al-Khuzai reported on the authority of her mother who said: I entered upon Umm Salamah and asked her about fasting. She said: The Messenger of Allah ﷺ used to command me to fast three days every month beginning with Monday or Thursday.